题解 | 喜欢

n,p = map(float,input().split())
s = list(map(float,input().split()))
res = 0
cur_p = 1

for i in range(int(n)):
    res += cur_p * p * s[i] * (i+1)
    cur_p *= 1-s[i]*p
res += cur_p * n
print(res)